Page 4 Drug and Gene Targeting Efficient Delivery of Agents to Molecular Targets unique features which are optimum under different targeting schemes. An example of use of a carbohydrate polymer is seen below when we delivered fluorescent phycobiliprotein linked to a multivalent carbohydrate polymer to the surface of activated endothelial cells in the flow loop apparatus. This is also a visualization of the first event of targeting when the delivered agent (phycobiliprotein) is bound to the cell surface through the carbohydrate polymer and is not internalization by the cells. The images are observations of the cells by fluorescent microscopy. The next example illustrates the second event of targeting in which the delivered agent has an effect on the endothelial cells. In this case, ricin, a potent toxin isolated from castor beans, binds to galactose-terminated oligosaccharides on the endothelial cell surface and is internalized leading to cell death. The cell death is visualized by use of a vital fluorescent dye which makes the cell fluorescent upon cell death. Digital imaging is used to count the number of dead cells, thus generating a killing kinetic profile for the targeted ricin. Similarly, a reporter gene, such as the gene for b-galactosidase (b-gal) or luciferase, could be targeted to the endothelial cells under flow and monitored for the expression of either protein by direct visualization of blue color (b-gal) or generation of fluorescence (luciferase).